Screening five local entomopathogenic nematode species for their virulence against pupae of the Eucalyptus snout beetle, Gonipterus sp. n. 2, under laboratory conditions

Abstract

The Eucalyptus snout beetle, Gonipterus sp. n. 2, is an important pest of eucalypt trees in South Africa and other countries. The pest is partially controlled with a mymarid egg parasitoid, Anaphes nitens. Identifying additional biological control agents that target other developmental stages of Gonipterus sp. n. 2 is necessary to improve control. Entomopathogenic nematodes (EPNs) are used as biological control agents for numerous soil pests and thus have the potential to be used against the pupal stage of Gonipterus sp. n. 2, which occurs in the soil. In this study, five South African EPN species were screened for their virulence on uncased pupae of Gonipterus sp. n. 2. At a concentration of 200 IJs/pupa in 50 μl of sterile water, Steinernema jeffreyense, S. fabii, Heterorhabditis noenieputensis and H. safricana caused pupal mortality of less than 40 %, while S. yirgalemense caused the highest pupal mortality of 100 % two days post-inoculation. Steinernema yirgalemense was selected and applied at different concentrations, namely 0, 12, 25, 50, 100, 200, and 400 IJs/pupa to determine its lethal concentration. Probit analysis indicated that the LC50 and LC90 of S. yirgalemense were 48.29 and 260.63 IJs/pupa, respectively. The study also showed that the pupal cases do not affect the efficacy of S. yirgalemense as it caused more than 90 % mortality of cased pupae of Gonipterus sp. n. 2 in soil bioassays. In addition, pupal age did not affect the efficacy of S. yirgalemense. Based on our findings, S. yirgalemense is a potential candidate for the biological control of pupae of Gonipterus sp. n. 2.